1. Field of the Invention
This invention relates to a drum brake device comprising a mechanical expander. More specifically, this invention related to a brake cable mounting structure in which an outer casing of the brake cable is attached on a stationary back plate.
2. Description of Prior Art
A brake cable functioning as a remote operation means for a drum brake generally mainly comprises an inner cable for operating a brake lever, being connected with a brake shoe facing an inner circumferential surface of the drum brake, and an outer casing for protecting the inner cable from an open air exposure. A cable end fixed at a tip end of the inner cable at a drum brake side engages with a free end of the brake lever; and a casing cap in stepped shape fixed on the outer casing at the end thereof, is attached on a stationary back plate facing a brake drum at an opening side thereof
A mounting section of the casing cap of the outer casing needs to have the following functions:
When the inner cable is pulled to operate the brake, a reaction force acts on the outer casing. Therefore, the outer casing needs to withstand the reaction force.
The drum brake is positioned at an unsprung portion of a vehicle while the operating side of the brake cable is positioned at a sprung portion of the vehicle. Hence, an operational direction of the reaction force acting on the mounting section of the casing cap slightly varies depending upon certain conditions such as vehicle weight and/or an air pressure of tires. Therefore, the outer casing needs to withstand such a biasing force.
Until the operating side of the brake cable is properly set in a vehicle body, i.e., when transporting the drum brake with the brake cable installed therein or mounting the same on the vehicle, if the outer casing is detached and moved toward the operating side of the brake cable, the inner cable is exposed out from the outer casing possibly causing a damage. Accordingly, the casing cap of the outer casing needs to be attached on the back plate so as to detach only if a predetermined external force is applied.
The outer casing needs to have an excellent waterproof function, because water ingress into the drum brake may deteriorate the brake performance.
In order to satisfy the above-requirements and needs, for example, the following structures are publicly disclosed:
A brake cable mounting structure of Provisional Japanese Patent Publication No. 6-337027 is characterized in that one end of a long tubular guide pipe extending in a brake axle direction is fixed on an anchor practically integrated with the back plate by affixation between an overhanging portion formed thereon and a widened end thereof; a small diameter column of a stepped casing cap slidably fits into the other end of the guide pipe at the outside of the brake until a large diameter over-hanging portion abuts thereagainst. A spring clip fits in an engagement groove of the small diameter column through a slit formed around the other end of the guide pipe; and thereafter the casing cap is fixed with the guide pipe to be practically integrated with the back plate.
Another brake cable mounting structure of Provisional Japanese Utility Model Publication No. 55-68734 is characterized in that the small diameter column of the stepped casing cap of the outer casing slidably fits into a back plate hole from the outside of the brake until a large diameter column abuts thereagainst; and a member, holding the small diameter column or the large diameter column both away from the fitting section, is fixed on the back plate.
That is, the casing cap is fixed on the back plate with two-point supporting and with the long span holing of the casing cap in an axial direction.
The conventional brake cable mounting structures for a drum brake have the following points to be improved.
The former invention, i.e., 6-337027, has problems in that it requires additional parts such as the tubular guide pipe and the spring clip and requires more time consuming and costly processes such as caulking the guide pipe on the back plate and cutting to form the slit in the guide pipe.
The latter invention, i.e., 55-68734, also has problems in that it requires additional parts such as the member to hold the casing cap of the outer casing and a bracket for fixing the casing cap on the back plate, thereby increasing the number of parts and making the mounting process more complex resulting in a higher cost of manufacturing.
This invention provides a brake cable mounting structure for a drum brake which has an excellent withstanding during the braking operation; does not possibly damage an inner cable while transporting the drum brake or mounting the same on a vehicle; and has an excellent waterproof function. Further, this invention provides a brake cable mounting structure for a drum brake of a simple structure with less number of parts and a lower cost.
In order to achieve the above-objects, in the brake cable mounting structure for a drum brake, the tubular member, for attaching the casing cap, is integrally formed on the back plate by pressing; and the casing cap of the outer casing is attached on the tubular member so as to detach only if a predetermined external force is applied.
The tubular member is integrally formed on a back plate by barring or processes of both drawing in a cup-shaped hollow and piercing to make a hole at a bottom of the drawn hollow.
In order to fit the casing cap of the outer casing in the tubular member on the back plate, the small diameter portion may be force-fit in the tubular member or a resilient ring putting in the ring-shaped groove of the small diameter portion may be resiliently fit in the tubular member.
Further, the tubular member may be stepped and integrally formed on the back plate.
The brake cable mounting structure for a drum brake as structured hereinabove realizes a long fitting section of the casing cap fitting the tubular portion of the back plate, thereby providing sufficient support to withstand the reaction force and biasing force acting on the outer casing. It also improves the waterproof function and prevents the damage to the inner cable because the casing cap is not detached unless the predetermined external force is applied. Accordingly, it provides a simple structured brake with the lower-cost.
The tubular member on the back plate may be integrally formed by pressing. Therefore, the processing of this portion is simple and is desirable for a mass production resulting in the lower manufacturing cost.
Fixing of the casing cap of the outer casing in the tubular member may be accomplished simply by pressing the casing cap into the tubular member, thereby facilitating the fixing process.
If the tubular member integrated with the back plate is formed in a stepped shape, the tubular member becomes longer, which may be applicable to various cable end to be fixed on the inner cable.